Up until today operators have been facing a challenge on how to avoid recompletion of wells where the nipple seal area inside the TRSCSSV (Tubing Retrievable Surface Controlled Subsurface Safety Valve) is damaged due to large amount of well interventions or damaged due to corrosion.
Various methods have been used for repairing a TRSCSSV with a damaged seal area. This includes standard insert WRSCSSV (Wireline Retrievable Surface Controlled Subsurface Safety Valve), with normal and oversize swell packing elements. Honing of the upper and lower seal area prior to installing an insert valve has also been performed but with variable success.
To have the DHSV working properly it is vital to maintain barrier control of the well. If the DHSV nipple profile is damaged the alternatives are to repair it using one of the above mentioned methods or to secure the well for later recompletion
Since all the above mentioned methods of repairing a damaged seal area for insert valve have failed, Statoil initiated a development project for a straddle design using well know element technology based on an HPHT Bridge Plug design. The straddle has solid elements, which shape according to the damage inside the seal areas. In addition each element is equipped with expanding anti-extrusion back-up rings on both sides, trapping the element so it has nowhere to go when differential pressure is applied. The straddle uses the existing nipple profile above the no-go for anchoring and is equipped with dogs to fit this profile. A standard insert safety valve is made up to the bottom of the straddle and is then operated by existing surface control line.
This paper will compare the different methods used for repairing a damaged Down Hole Safety Valve nipple seal area and discuss the development process and qualification testing done for the new unique straddle system and setting tool. Case histories will also be presented from several prolific North Sea Wells.